Magnetic disk and manufacturing method thereof

ABSTRACT

A magnetic disk of is provided, the magnetic disk having at least a magnetic layer, a carbon protective layer, and a lubrication layer sequentially provided on a substrate. In an embodiment, the lubrication layer a film formed by a lubricant having a perfluoropolyether compound A having a perfluoropolyether main chain in the structure and also having a hydroxyl group at the end and a compound C obtained from a reaction between a compound B expressed by: [Chemical formula 1] CF 3 (—O—C 2 F 4 )m-(O—CF 2 )n-OCF 3  [m and n in the formula are natural numbers.] and aluminum oxide.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Ser. No. 13/121,901, filed Jun. 20,2011, which is a National Stage of International Application No.PCT/JP2009/067022 filed Sep. 30, 2009 claiming benefit of Japanesepriority Application No. JP2008-254128 filed on Sep. 30, 2008, and ofJapanese priority Application No. JP2008-254130 filed on Sep. 30, 2008,and of Japanese priority Application No. JP2008-259136 filed on Oct. 4,2008, the contents of all of which (including chemical formulas) areincorporated herein by reference in their entirety.

TECHNICAL FIELD

The present invention relates to a magnetic disk mounted on a magneticdisk device such as a hard disk drive (hereinafter referred to as HDD).

BACKGROUND ART

With the recent trend to higher-capacity information processing, variousinformation recording technologies have been developed. Particularly, asurface recording density of an HDD using the magnetic recordingtechnology has been continuously increased by a rate of approximately100% a year. In recent years, an information recording capacityexceeding 250 GB per disk is required for a magnetic disk having aradius of 2.5 inch used in HDD or the like, and in order to meet suchdemand, realization of an information recording density exceeding 400Gbits per 1 square inch is in demand. In order to achieve the highrecording density in a magnetic disk used in an HDD or the like,magnetic crystal grains constituting a magnetic recording layer handlingrecording of an information signal need to be refined, and its layerthickness needs to be reduced at the same time. However, in the case ofa magnetic disk of an in-plane magnetic recording method (also referredto as longitudinal magnetic recording method or horizontal magneticrecording method) having been merchandized, as the result of developmentof the refining of the magnetic crystal grains, thermal stability of therecording signal is damaged by a superparamagnetic phenomenon, and therecording signal is lost. A thermal fluctuation phenomenon begins tooccur, which makes an obstructive factor to higher recording density ofa magnetic disk.

In order to solve this obstructive factor, a magnetic recording mediumof a perpendicular magnetic recording method has been proposed recently.In the case of the perpendicular magnetic recording system, differentfrom the in-plane magnetic recording method, a magnetization easy axisof a magnetic recording layer is adjusted to be oriented in theperpendicular direction with respect to a substrate surface. As comparedwith the in-plane recording method, the perpendicular magnetic recordingmethod can suppress the thermal fluctuation phenomenon, which issuitable for higher recording density. This type of perpendicularmagnetic recording mediums include a so-called two-layer typeperpendicular magnetic recording disk provided with a soft magneticunderlayer made of a soft magnetic body on a substrate and aperpendicular magnetic recording layer made of a hard magnetic body.

In a prior-art magnetic disk, a protective layer and a lubrication layerare provided on the magnetic recording layer formed on a substrate inorder to ensure durability and reliability of the magnetic disk.Particularly, the lubrication layer used on the outermost surfacerequires various characteristics such as long-term stability, chemicalsubstance resistance, friction resistance, heat resistant properties andthe like.

In response to such request, a perfluoropolyether lubricant having ahydroxyl group in a molecule has been widely used as a lubricant formagnetic disk. For example, as in Japanese Patent Laid-Open No.S62-66417 (Patent Document 1), a magnetic recording medium on which aperfluoroalkylpolyether lubricant having a structure ofHOCH₂CF₂O(C₂F₄O)_(p)(CF₂O)_(q)CH₂OH having a hydroxyl group at both endsof the molecule is applied is well known. If there is a hydroxyl groupin a molecule of a lubricant, it is known that an adhesioncharacteristic to a protective layer of the lubricant can be obtained byan interaction of the protective layer and the hydroxyl group.

CITATION LIST Patent Literature

PTL 1: Japanese Unexamined Patent Application Publication No. S62-66417

SUMMARY OF INVENTION Technical Problem

As described above, the information recording density of 400 Gbits/inch²or more is required for the recent HDD, but one of the reasons for thatis, in addition to the needs for an HDD as a conventional storage devicefor computer, related to applications by being mounted on a mobilephone, a car-navigation system, a digital camera and the like. In thecase of these new applications, a housing space on which the HDD ismounted is extremely smaller than that of a computer, thus the size ofthe HDD needs to be reduced. For that purpose, a diameter of a magneticdisk to be mounted on the HDD needs to be reduced. In the computerapplication, for example, a 3.5-inch type or 2.5-inch type magnetic diskcan be used, but in the case of the above new applications, asmaller-sized such as a 1.8-inch to 0.8-inch type small-diametermagnetic disk is used, for example. Even if the diameter of the magneticdisk is reduced, a certain level or more of an information capacityneeds to be stored, which increasingly promotes improvement of theinformation recording density.

Also, in order to effectively utilize a limited disk area, an LUL (LoadUnload) method HDD has begun to be used instead of the prior-art CSS(Contact Start and Stop) method. In the LUL method, when an HDD isstopped, a magnetic head is retreated onto an inclined base called aramp located outside the magnetic disk and in a start operation, afterthe magnetic disk starts rotating, the magnetic head is made to slidefrom the ramp onto the magnetic disk, floated and flied for recordingand reproducing. In a stop operation, the magnetic head is retreated tothe ramp outside the magnetic disk and then, the rotation of themagnetic disk is stopped. This series of operations are called LULoperations. In a magnetic disk to be mounted on the LUL-method HDD, acontact sliding region (CSS region) with the magnetic head as in the CSSmethod does not have to be provided, and thus, a recording andreproducing area can be expanded, which is preferable for a higherinformation capacity.

In order to improve the information recording density under thesecircumstances, a spacing loss needs to be reduced as much as possible byreducing a floating amount of the magnetic head. In order to achieve theinformation recording density of 100 Gbits or more per 1 square inch,the floating amount of the magnetic head needs to be within 10 nm. Inthe LUL method, unlike the CSS method, a projection and recess shape forthe CSS does not have to be provided on the magnetic disk surface,whereby the magnetic disk surface can be extremely smoothened. Thus, inthe magnetic disk to be mounted on the LUL method HDD, the magnetic-headfloating amount can be further lowered as compared with the CSS method,whereby a higher S/N ratio of the recording signal can be realized, andcontribution can be made to a higher recording capacity of a magneticdisk device, which is an advantage.

Due to the further decrease of the magnetic-head floating amountpromoted by recent introduction of the LUL method, a stable operation ofthe magnetic disk even with a low floating amount not more than 10 nm isin demand at present. Particularly, as described above, the magneticdisk has been moving from the in-plane magnetic recording method to theperpendicular magnetic recording method, and a larger capacity of amagnetic disk and a decrease in a flying height with that are in strongdemand.

As described above, in recent years, the magnetic disk devices arewidely used not only as a storage device of a conventional personalcomputer but in mobile applications including a mobile phone and acar-navigation system, and due to diversification of the applications,environmental resistances required for the magnetic disk has beenextremely severe. Therefore, in terms of these situations, furtherimprovement of durability of the magnetic disk or durability of alubricant constituting a lubrication layer is imminent.

Also, with the recent rapid improvement of the information recordingdensity of the magnetic disk, reduction of a magnetic spacing betweenthe magnetic head and the recording layers of the magnetic disk is indemand, and a lubrication layer located between the magnetic head and arecording layer of the magnetic disk needs to be further thinned. Alubricant used for the lubrication layer on the outermost surface of themagnetic disk has a large influence on durability of the magnetic disk,but even if it is made into a thin film, stability and reliability areindispensable for the magnetic disk.

As described above, realization of a magnetic disk excellent inlong-term stability of a lubrication layer and having a reduced magneticspacing with the recent higher recording density and high reliabilitywith a decreased floating amount of the magnetic head is in demand, anddue to diversification of the applications and the like, environmentalresistance required for the magnetic disk has become extremely severe,and thus, further improvement of the characteristics such as durabilityof a lubricant constituting a lubrication layer largely affectingdurability of the magnetic disk and particularly LUL durability and afixed-point floating characteristic (CFT characteristic) is in demand.

The present invention was made in view of the above conventionalsituations and has an object to provide a magnetic disk excellent indurability of the magnetic disk or particularly in LUL durability andCFT characteristics and having high reliability under a decreasedfloating amount of the magnetic head accompanying the recent rapidincrease in a recording density and extremely severe environmentalresistance accompanying diversification of the applications.

Solution to Problem

The inventors have examined adhesion properties of a lubricant largelyaffecting durability of a lubricant to a protective layer. In the caseof a prior-art lubricant having a hydroxyl group at ends of a molecule,after the lubricant is applied on a disk, chemical binding is generatedbetween the protective film and the hydroxyl group by baking treatment,and the adhesion properties of the lubricant to the protective layer isobtained, but at this time, not all the active points (adsorptionpoints) on the protective film are involved with the binding with thelubricant. If this type of magnetic disk is used by being mounted on amagnetic disk device, the active points on the protective film notinvolved with the binding with the lubricant gradually suck an organicgas mainly consisting of a Si gas and the like in the atmosphere, andparticularly with a low floating amount, organic contamination or thelike adsorbed onto the surface of the lubrication layer is highly likelyto transfer to a magnetic head and as a result, causes a fly stictionfailure due to head contamination.

The inventors have found out that the above problems can be solved bythe following invention through keen examination and completed thepresent invention.

That is, the present invention has the following configuration.

(Composition 1) A magnetic disk having at least a magnetic layer, aprotective layer, and a lubrication layer sequentially provided on asubstrate, in which the lubrication layer is a film formed by alubricant that contains two types of compounds having aperfluoropolyether main chain in the structure, a molecular weightdistribution of the two types in total being within a range of 1 to 1.2,the two types of compounds including a compound a having a hydroxylgroup at the end and a compound b having a number average molecularweight smaller than the number average molecular weight of the compounda and not more than 1500, and a content of the compound b in the twotypes of compounds being not more than 10%.

(Composition 2) The magnetic disk described in the composition 1,characterized in that the number average molecular weight of thecompound a is within a range of 1000 to 10000.

According to the invention according to the composition 1, since thelubricant contains the compound b having a low molecular weight, activepoints on the protective film not binding with the lubricant compound ahaving a high molecular weight binds with the compound b having a lowmolecular weight, and as a result, by means of the decrease in theactive points on the protective film not binding with the lubricant, itis possible to suppress adsorption of organic contamination, and amagnetic disk in which occurrence of a fly stiction failure issuppressed, characteristics such as the LUL durability and CFTcharacteristics of the magnetic disk are more excellent than before, andunder the low floating amount of the magnetic head accompanying therecent rapid increase in a recording density, a magnetic disk havinghigh reliability under the extremely severe environmental resistanceaccompanying diversified applications can be obtained.

Here, as described in the invention according to the composition 2, thenumber average molecular weight of the lubricant compound a contained inthe lubrication layer is particularly preferably within the range of1000 to 10000. That is because repairability by appropriate viscosity isprovided, favorable lubrication performances are exerted, and excellentheat resistance can be also provided.

(Composition 3) A magnetic disk having at least a magnetic layer, aprotective layer, and a lubrication layer sequentially provided on asubstrate, characterized in that the lubrication layer contains acompound having a perfluoropolyether main chain in the structure, themolecular weight distribution of the compound is within a range of 1 to1.2 and the content of the one with the number average molecular weightnot more than 1500 is not more than 10%.

(Composition 4) The magnetic disk described in the composition 3, inwhich the compound is a compound having a hydroxyl group at the end ofthe molecule.

(Composition 5) The magnetic disk described in the composition 3 or 4,in which the number average molecular weight of the compound containedin the lubrication layer is within a range of 1000 to 10000.

(Composition 6) The magnetic disk described in any one of thecompositions 3 to 5, in which the protective layer is a carbonprotective layer formed by a plasma CVD method.

(Composition 7) The magnetic disk described in any one of thecompositions 3 to 6, in which the magnetic disk is a magnetic diskmounted on a magnetic disk device of a load-unload method.

(Composition 8) A manufacturing method of a magnetic disk having atleast a magnetic layer, a protective layer, and a lubrication layersequentially provided on a substrate, characterized in that thelubrication layer is a film formed by performing molecular distillationof a lubricant containing a perfluoropolyether compound having aperfluoropolyether main chain in the molecule and by forming a film ofthe lubricant having a molecular weight distribution of the compoundwithin a range of 1 to 1.2 and a content of the one with a numberaverage molecular weight of not more than 1500 is not more than 10% onthe protective layer.

(Composition 9) The manufacturing method of a magnetic disk described inthe composition 8, characterized in that after the film of thelubrication layer is formed, the magnetic disk is exposed to anatmosphere of 50 to 150° C.

According to the invention according to the composition 3, since themolecular weight distribution of the lubricant compound includes alow-molecular region side and contains the low-molecular-weightlubricant compound, the active points on the protective film that didnot bind with the high-molecular-weight lubricant compound binds withthe low-molecular-weight lubricant compound, and the active points notbinding with the lubricant on the protective film are reduced as aresult, whereby adsorption of organic contamination can be suppressed,occurrence of a fly stiction failure can be deterred, and thecharacteristics such as the LUL durability and the CFT characteristicsof the magnetic disk is made more excellent than before, and under thelower floating amount of the magnetic head accompanying the recent rapidincrease in a recording density and under the extremely severeenvironmental resistance accompanying the diversification ofapplications, a magnetic disk with high reliability can be obtained.

As in the invention according to the composition 4, the compoundcontained in the lubrication layer is particularly preferably a compoundcontaining a hydroxyl group at the end of the molecule. The hydroxylgroup greatly interacts with the protective layer or particularly acarbon protective layer, which improves adhesion properties between thelubrication layer and the protective layer.

Also, as described in the invention according to the composition 5, thenumber average molecular weight of the compound contained in thelubrication layer is particularly preferably within the range of 1000 to10000. That is because repairability by appropriate viscosity isprovided, favorable lubrication performances are exerted, and excellentheat resistance can be also provided.

Also, as described in the invention according to the composition 6, theprotective layer is particularly preferably a carbon protective layer, afilm formed by the plasma CVD method. By means of the plasma CVD method,a carbon protective layer, which is a film closely formed having auniform surface, can be formed, which is preferable for the presentinvention.

Also, as described in the invention according to the composition 7, themagnetic disk of the present invention is particularly preferable as amagnetic disk mounted on a LUL-method magnetic disk device. A furtherdecrease of the magnetic-head floating amount realized by introductionof the LUL method has required the magnetic disk to operate stably evenwith a low floating amount of not more than 10 nm, and the magnetic diskof the present invention having high reliability under the low floatingamount is preferable.

Also, as described in the invention according to the composition 8, themagnetic disk of the present invention having high reliability under thelow floating amount is a manufacturing method of a magnetic disk inwhich at least a magnetic layer, a protective layer, and a lubricationslayer are sequentially provided on a substrate, and the lubricationlayer is preferably obtained by the manufacturing method of a magneticdisk formed by performing molecular distillation of a lubricantcontaining a perfluoropolyether compound having a perfluoropolyethermain chain in the molecule and by forming a film of the lubricant havinga molecular weight distribution of the compound within a range of 1 to1.2 and a content of the one with a number average molecular weight ofnot more than 1500 is not more than 10% on the protective layer.

Also, as described in the invention according to the composition 9, inthe manufacturing method of the magnetic disk of the composition 8,after the lubrication layer is formed, by exposing the magnetic disk tothe atmosphere at 50 to 150° C., the adhering force of the formedlubrication layer to the protective layer can be further improved.

(Composition 10) A magnetic disk having at least a magnetic layer, aprotective layer, and a lubrications layer sequentially provided on asubstrate, in which the lubrication layer is a film formed by alubricant containing a perfluoropolyether compound a having aperfluoropolyether main chain in the structure and a hydroxyl group atthe end and a compound b with the number average molecular weight notmore than 1500 having a perfluoropolyether main chain in the structureand an aromatic group at both ends of the hydroxyl group and achain-state molecule.

(Composition 11) The magnetic disk described in the composition 10,characterized in that the number average molecular weight of thecompound a contained in the lubrication layer is within a range of 1000to 10000.

(Composition 12) The magnetic disk described in the composition 10 or11, characterized in that the protective layer is a carbon protectivelayer, which is a film formed by the plasma CVD method.

(Composition 13) The magnetic disk described in any one of thecomposition 10 to 12, characterized in that the magnetic disk is amagnetic disk mounted on a Load-Unload method magnetic disk device.

According to the invention according to the composition 10, since thelubrication layer is a film formed by a lubricant formed containing aperfluoropolyether compound a (hereinafter referred to as lubricantcompound a) having a perfluoropolyether main chain in the structure anda hydroxyl group at the end and a compound b with the number averagemolecular weight not more than 1500 having a perfluoropolyether mainchain in the structure and an aromatic group at both ends of thehydroxyl group and a chain-state molecule, the low-molecular-weightcompound b having both the hydroxyl group with a strong adsorbing forcewith the active points on the protective film and the aromatic groupthat can interact with the active points on a relatively wide rangeenters a spatial gap of the high-molecular-weight lubricant compound aand efficiently bind with the active points on the protective film notbinding with the high-molecular-weight lubricant compound a so as toreduce the active points on the protective film not binding with eitherof the lubricant compound a or compound b as a result, wherebyadsorption of organic contamination can be suppressed, and a magneticdisk, in which occurrence of a fly stiction failure is suppressed, canbe obtained which is more excellent in the characteristics such as theLUL durability and CFT characteristics of the magnetic disk than beforeand has high reliability under the low floating amount of the magnetichead accompanying the recent rapid increase in a recording density andmoreover under the extremely severe environmental resistanceaccompanying the diversification of applications.

Also, as in the invention according to the composition 11, the numberaverage molecular weight of the compound a contained in the lubricationlayer is particularly preferably within a range of 1000 to 10000. Thatis because repairability by appropriate viscosity is provided, favorablelubrication performances are exerted, and excellent heat resistance canbe also provided.

Also, as in the invention according to the composition 12, theprotective layer is particularly preferably a carbon protective layer, afilm formed by the plasma CVD method. By means of the plasma CVD method,a carbon protective layer, which is a film closely formed having auniform surface, can be formed, which is preferable for the presentinvention.

Also, as described in the invention according to the composition 13, themagnetic disk of the present invention is particularly preferable as amagnetic disk mounted on a LUL-method magnetic disk device. A furtherdecrease of the magnetic-head floating amount realized by introductionof the LUL method has required the magnetic disk to operate stably evenwith a low floating amount of not more than 10 nm, and the magnetic diskof the present invention having high reliability under the low floatingamount is preferable.

(Composition 14) A magnetic disk in which at least a magnetic layer, aprotective layer, and a lubrication layer are sequentially provided on asubstrate, in which the lubrication layer is a film formed by alubricant having a perfluoropolyether compound a having aperfluoropolyether main chain in the structure and also having ahydroxyl group at the end and a compound c obtained from a reactionbetween a compound b expressed by:

[Chemical formula 1]CF₃(—O—C₂F₄)m—(O—CF₂)n—OCF₃ [m and n in the formula are naturalnumbers.]

and aluminum oxide.

(Composition 15) The magnetic disk described in the composition 14,characterized in that the number average molecular weight of thecompound a contained in the lubrication layer is within a range of 1000to 10000.

(Composition 16) The magnetic disk described in the composition 14 or15, characterized in that the protective layer is a carbon protectivelayer, which is a film formed by the plasma CVD method.

(Composition 17) The magnetic disk described in any one of thecomposition 14 to 16, characterized in that the magnetic disk is amagnetic disk mounted on an Load-Unload method magnetic disk device.

According to the invention according to the composition 14, since thelubrication layer is a film formed by a lubricant having aperfluoropolyether compound a (hereinafter referred to as a lubricantcompound a) having a perfluoropolyether main chain in the structure andalso having a hydroxyl group at the end and a low-molecular-weightcompound c obtained from the reaction between a compound b and aluminumoxide, the low-molecular-weight compound c enters a spatial gap of thehigh-molecular-weight lubricant compound a and binds with the activepoints on the protective film not binding with the high-molecular-weightlubricant compound a so as to reduce the active points on the protectivefilm not binding either of the lubricant compound a or compound c as aresult, whereby adsorption of organic contamination can be suppressed,occurrence of a fly stiction failure is suppressed, and a magnetic diskcan be obtained which is more excellent in the characteristics such asthe LUL durability and CFT characteristics of the magnetic disk thanbefore and has high reliability under the low floating amount of themagnetic head accompanying the recent rapid increase in a recordingdensity and moreover under the extremely severe environmental resistanceaccompanying the diversification of applications.

Also, as in the invention according to the composition 15, the numberaverage molecular weight of the compound a contained in the lubricationlayer is particularly preferably within a range of 1000 to 10000. Thatis because repairability by appropriate viscosity is provided, favorablelubrication performances are exerted, and excellent heat resistance canbe also provided.

Also, as in the invention according to the composition 16, theprotective layer is particularly preferably a carbon protective layer, afilm formed by the plasma CVD method. By means of the plasma CVD method,a carbon protective layer, which is a film closely formed having auniform surface, can be formed, which is preferable for the presentinvention.

Also, as described in the invention according to the composition 17, themagnetic disk of the present invention is particularly preferable as amagnetic disk mounted on a LUL-method magnetic disk device. A furtherdecrease of the magnetic-head floating amount realized by introductionof the LUL method has required the magnetic disk to operate stably evenwith a low floating amount of not more than 10 nm, and the magnetic diskof the present invention having high reliability under the low floatingamount is preferable.

Advantageous Effects of Invention

According to the present invention, a magnetic disk excellent in thedurability of the magnetic disk or particularly in the LUL durabilityand CFT characteristics and having high reliability (a stable operationcan be guaranteed) under the low floating amount of the magnetic headaccompanying the recent rapid increase in a recording density andmoreover under the extremely severe environmental resistanceaccompanying the diversification of applications.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic sectional view of an embodiment of a magnetic diskof the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention will be described below in detail.

The magnetic disk of the present invention is a magnetic disk, as in thecomposition 1, having at least a magnetic layer, a protective layer, anda lubrication layer sequentially provided on a substrate, in which thelubrication layer is a film formed by a lubricant containing two typesof compounds having a perfluoropolyether main chain in the structure, amolecular weight distribution of the two types in total is within arange of 1 to 1.2, the two types of compounds including a compound ahaving a hydroxyl group at the end and a compound b having a numberaverage molecular weight smaller than the number average molecularweight of the compound a and not more than 1500, and a content of thecompound b in the two types of compounds being not more than 10%.

According to the above invention, since the lubricant contains thecompound b having a low molecular weight, active points on theprotective film not binding with the lubricant compound a having a highmolecular weight binds with the compound b having a low molecularweight, and as a result, by means of the decrease in the active pointson the protective film not binding with the lubricant, it is possible tosuppress adsorption of organic contamination, and a magnetic disk inwhich occurrence of a fly stiction failure is suppressed,characteristics such as the LUL durability and CFT characteristics ofthe magnetic disk are more excellent than before, and under the lowfloating amount of the magnetic head accompanying the recent rapidincrease in a recording density, and having high reliability under theextremely severe environmental resistance accompanying diversifiedapplications can be obtained.

Here, the number average molecular weight of the lubricant compound acontained in the lubrication layer is particularly preferably within therange of 1000 to 10000. That is because repairability by appropriateviscosity is provided, favorable lubrication performances are exerted,and excellent heat resistance can be also provided.

In order to have the advantages of the present invention exertedfavorably, a difference in the molecular weight between the lubricantcompound a having a high molecular weight and the compound b having alower molecular weight is preferably within a range of approximately 500to 2000 in a number average molecular weight.

As the present invention, the following embodiment is preferable.

Subsequently, embodiments of the present invention will be described inmore detail.

First Embodiment

A magnetic disk according to a first embodiment of the present inventionis a magnetic disk having at least a magnetic layer, a protective layer,and a lubrication layer sequentially provided on a substrate, in whichthe lubrication layer contains a compound having a perfluoropolyethermain chain in the structure, a molecular weight distribution of thecompound is within a range of 1 to 1.2, and a content of the one with anumber average molecular weight not more than 1500 is not more than 10%.

The lubricant compound contained in the lubrication layer in themagnetic disk of the present invention is a compound having aperfluoropolyether main chain in the structure and a compound(hereinafter referred to as a lubricant compounds (I) according to thepresent invention) expressed by the following chemical formula, forexample:

[p and q in the formula are natural numbers.]

or a compound (hereinafter referred to as a lubricant compounds (II)according to the present invention) expressed by the following chemicalformula:

[Chemical formula 3]HO—CH₂—CF₂(—O—C₂F₄)m—(O—CF₂)n—OCF₂—CH₂—OH

[m and n in the formula are natural numbers.]

Also, in addition to the above, a compound (hereinafter referred to as alubricant compounds (III) according to the present invention) having aperfluoropolyether main chain in the structure and perfluoropolyethergroups having a hydroxyl group at the end binding with each other via alinking group having at least a hydroxyl group in the structure ispreferably named.

The lubricant compound (I) according to the present invention containedin the lubrication layer in the magnetic disk of the present inventionis a perfluoropolyether compound having a perfluoropolyether main chainin the structure and having four hydroxyl groups at the end. Also, thelubricant compound (II) according to the present invention is aperfluoropolyether compound having a perfluoropolyether main chain inthe structure and having two hydroxyl groups at the end. As theseperfluoropolyether lubricants, commercial products including FomblinZ-TETRAOL (product name) and Fomblin Z DOL (product name) by SOLVAYSOLEXIS, Inc., for example, can be used.

Also, the lubricant compound (III) according to the present invention isa compound having a perfluoropolyether main chain in the structure andperfluoropolyether groups having a hydroxyl group at the end bindingwith each other via a linking group having at least a hydroxyl group inthe structure, and it is only necessary that the linking group has atleast a hydroxyl group in the structure and has a group expressed as—(CR₁R₂)—, for example. Here, R₁ and R₂ are hydrogen atoms or hydroxylgroups, respectively.

The above perfluoropolyether group has a perfluoropolyether main chainexpressed as —(O—C₂F₄)m-(O—CF₂)n- (m and n are both integers not lessthan 1) in the structure and also having a hydroxyl group at the end,for example, and as such perfluoropolyether group, a group expressed bythe following formula (I) is preferably named:

Formula (I)

[Chemical formula 4]HOCH₂CF₂(OC₂F₄)m(OCF₂)nOCF₂CH₂O—  

In the formula, m and n are both integers not less than 1.

As a manufacturing method of the lubricant compound (III) according tothe present invention, a manufacturing method of reacting 2 equivalentweight or 3 equivalent weight to the perfluoropolyether compound havinga perfluoropolyether main chain in a molecule and having a hydroxylgroup at the end with 1 equivalent weight of an aliphatic compoundhaving the structure that can react with the perfluoropolyether compoundand generate a hydroxyl group, for example, is preferably cited. As thealiphatic compound, for example, a diepoxy compound having an epoxidostructure at the end is preferably named. By using such compound, thelubricant compound (III) according to the present invention can beobtained with high purity and high yield. Specific examples of suchdiepoxy compounds are named below but they do not limit the presentinvention.

Also, as the above perfluoropolyether compound, a perfluorodiol compoundhaving a hydroxyl group at the molecule end and expressed by thefollowing formula (II) is cited:

Formula (II)

[Chemical formula 6]HOCH₂CF₂(OC₂F₄)m(OCF₂)nOCF₂CH₂OH  

In the formula, m and n are both integers not less than 1.

That is, under a base condition, by having a perfluoropolyether compoundhaving a hydroxyl group at the end work on the base so as to havealkoxide, and this alkoxide develops a nucleophillic open-chain reactionwith an aliphatic compound having an epoxide structure at the end andthen, a 2 equivalent amount or 3 equivalent amount compound in which theperfluoropolyether compounds bind with each other through a linkinggroup changed from the above aliphatic compound is obtained.

Examples of the lubricant compound (III) according to the presentinvention are cited below, but the present invention is not limited bythese compounds:

Rf: —(OC₂F₄)m(OCF₂)n- (m, n=integer not less than 1)

In the present invention, as the lubricant constituting the lubricationlayer, the lubricant compounds (I), (II), and (III) according to thepresent invention may be used singularly or they may be mixed asappropriate and used. Combinations when being used in a mixture isarbitrary.

In the present invention, by performing molecular weight fractionationwith an appropriate method, molecular weight distribution (weightaverage molecular weight (Mw)/number average molecular weight (Mn)ratio) of the lubricant compounds contained in the lubrication layerwithin a range of 1 to 1.2 and also a content of a compound having thenumber average molecular weight not more than 1500 is not more than 10%.Particularly preferably, molecular weight distribution within a range of1 to 1.2 and also a compound having the number average molecular weightwithin a range of 800 to 1500 is contained in a range of 5 to 10%.

The lubricant compound contained in the lubrication layer of the presentinvention contains, in short, two types of compounds, that is, acompound with a high molecular weight having a perfluoropolyether mainchain in the structure and a compound with a low molecular weight, andthe molecular weight distribution of the two types of the compounds intotal is within the range of 1 to 1.2. The two types of the compoundsinclude a compound a with a high molecular weight preferably having ahydroxyl group at an end and a compound b with a molecular weight lowerthan the compound a, that is, with a number average molecular weightsmaller than the compound a and not more than 1500. And a content of thecompound b in these two types of the compounds is not more than 10%.

Regarding conventional lubricants, molecular weight fractionation iscarried out such that the molecular weight distribution becomes asnarrow as possible and the low-molecular region side is removed, but ifa lubrication layer is formed by using such lubricant, many of theactive points on the protective film not involved in binding with thelubricant remain, which causes occurrence of a fly stiction failure dueto adsorption of organic contamination.

On the other hand, in the present invention, since the molecular weightdistribution of the lubricant compound includes a low-molecular regionside and contains the lubricant compound with a low molecular weight,the active points on the protective film not binding with the lubricantcompound with a high molecular weight bind with the lubricant compoundwith a low molecular weight, and the active points on the protectivefilm not binding with the lubricant are decreased as a result, and thus,adsorption of organic contamination can be suppressed, and occurrence ofa fly stiction failure is suppressed. As a result, under a decreasedfloating amount of the magnetic head accompanying the recent rapidincrease in a recording density, and moreover under an extremely severeenvironmental resistance accompanying the diversified applications, amagnetic disk having high reliability can be obtained.

In the present invention, there is no need to limit a method of carryingout molecular weight fractionation, but molecular weight fractionationusing a gel permeation chromatography (GPC) method or molecular weightfractionation using a supercritical extraction method can be used, forexample.

The molecular weight of the lubricant according to the present inventionis not particularly limited, but the number average molecular weight(Mn) is preferably within a range of 1000 to 10000, for example, or morepreferably within a range of 1000 to 6000. That is because repairabilityby appropriate viscosity is provided, and favorable lubricationperformances can be exerted.

Since the lubricant compound (III) according to the present invention ismade of a compound in which perfluoropolyether compounds bind with eachother through a linking group, a compound with a high molecular weightof 2 equivalent or 3 equivalent to perfluoropolyether is obtained, andsince a decrease in the molecular weight by thermal decomposition can besuppressed, a magnetic disk using such lubricant can have its heatresistance improved. With a further decrease (10 nm or less) in thefloating amount of the magnetic head accompanying the recent increase ina recording density, a possibility of frequent contact and frictionbetween the magnetic head and the magnetic disk surface is getting high.Also, in the case of the contact with the magnetic head, it is likelythat the magnetic head does not depart from the magnetic disk surfaceimmediately but remains in friction and sliding. Also, due to recordingand reproducing by the recent high-speed rotation of the magnetic disk,more heat is generated than before by contact and friction. Therefore, apossibility of thermal decomposition of a lubricant layer material onthe magnetic disk surface becomes higher than before due to thegeneration of heat as above, and adhesion of the thermally-decomposedlubricant with lowered molecular weight and increased fluidity to themagnetic head, reading/writing of data might be hindered. Moreover,considering data recording and reproducing in a near future in a statein which the magnetic head is in contact with the magnetic disk, aninfluence of heat generated by contact all the time is furtherconcerned. In view of these circumstances, further improvement on heatresistance required for the lubrication layer is in demand, and thelubricant compound (III) is particularly favorable.

In forming a film of the lubrication layer using the lubricant accordingto the present invention, the film can be formed by applying by a dipmethod, for example, using a solution in which the lubricant isdispersed and dissolved in an appropriate solvent. As the solvent, afluorine solvent (Vertrel XF by DU PONT-MITSUI FLUOROCHEMICALS COMPANY,LTD. or the like), for example, can be favorably used. The film formingmethod of the lubrication layer is naturally not limited to the abovedip method but a film forming method such as a spin coating method, aspraying method, a paper coating method and the like may be used.

In the present invention, in order to further improve an adhesion forceof the formed lubrication layer to the protective layer, the magneticdisk may be exposed to the atmosphere at 50 to 150° C. after the filmformation.

In the present invention, the film thickness of the lubrication layer ispreferably 5 to 20 Å. If it is less than 5 Å, lubrication performancesas the lubrication layer might be lowered. The thickness exceeding 20 Åis not preferable from the viewpoint of film thinning.

Second Embodiment

A magnetic disk according to a second embodiment of the presentinvention is a magnetic disk having at least a magnetic layer, aprotective layer, and a lubrication layer sequentially provided on asubstrate, in which the lubrication layer is constituted by forming afilm of a lubricant containing a lubricant compound a and a compound bhaving a perfluoropolyether main chain in the structure, a hydroxylgroup and an aromatic group at both ends of a chain-state molecule, anda number average molecular weight not more than 1500.

The lubricant compound a contained in the lubrication layer in themagnetic disk of the present invention is a perfluoropolyether compoundhaving a perfluoropolyether main chain in the structure and a hydroxylgroup at the end, and a compound expressed by the following chemicalformula, for example, is favorably cited:

[p and q in the formula are natural numbers.]

The above exemplary compound of the lubricant compound a contained inthe lubrication layer in the magnetic disk of the present invention is aperfluoropolyether compound having a perfluoropolyether main chain inthe structure and having four hydroxyl groups at the end. Also, as thelubricant compound a according to the present invention, aperfluoropolyether compound having a perfluoropolyether main chain inthe structure and having two hydroxyl groups at the end can be alsoused. As these perfluoropolyether lubricants, commercial productsincluding Fomblin Z-TETRAOL (product name) and Fomblin Z DOL (productname) by SOLVAY SOLEXIS, Inc., for example, can be used.

Also, the compound b contained in the lubricant for forming thelubrication layer in the present invention is a compound having aperfluoropolyether main chain in the structure and also having ahydroxyl group and an aromatic group at the both ends of a chain-statemolecule and with the number average molecular weight of not more than1500.

As the aromatic group in this case, a phenyl group, for example, can becited as a typical example, but a naphthylene group, a biphenyl group, aphthalimidyl group, an aniline group and the like can be also cited. Thearomatic group may have an appropriate substituent group.

The compound b contained in the lubrication layer together with thelubricant compound a as above is a compound having an aromatic groupsuch as a phenyl group at both ends of a chain-state molecule having aperfluoropolyether main chain in the structure, for example, and inorder that the working effects by the present invention is exertedfurther favorably, it is preferably a compound having a hydroxyl groupother than the aromatic group in the structure. The compound isparticularly preferably a compound having both the aromatic group andthe hydroxyl group at the both ends of the chain-state molecule having aperfluoropolyether main chain in the structure.

The exemplary compounds of the compound b according to the presentinvention are cited below, but the present invention is not limited bythese compounds:

(m, n=integer not less than 1)

(m, n=integer not less than 1)

(m, n=integer not less than 1)

(m, n=integer not less than 1)

As the manufacturing method of the compound b according to the presentinvention, a manufacturing method in which 2 equivalent weight of acompound (glycidyl phenyl ether, for example) having an epoxy group andan aromatic group, for example, is made to react with theperfluoropolyether compound having a perfluoropolyether main chain inthe molecule, for example, is favorably cited.

The above compound having an epoxy group and an aromatic group is notparticularly limited, and the following compounds and the like can becited, for example.

Regarding the molecular weight of the compound b according to thepresent invention, the number molecular weight (Mn) thereof ispreferably within a range not more than 1500, for example, or morepreferably within a range of 500 to 1500 in order that the workingeffects of the present invention is favorably exerted.

In the present invention, as the lubricant that forms a lubricationlayer, the above lubricant compound a and the above compound b are mixedin use. A mixing ratio when being used in a mixture is preferably suchthat a weight ratio of the lubricant compound a/compound b is within arange of approximately 8:2 to 9:1. If the rate of the lubricant compounda in the lubricant is smaller than the above range, favorablelubrication performances might not be obtained. Also, if the rate of thecompound b in the lubricant is smaller than the above range, the workingeffect that the compound b with a low molecular weight efficiently bindswith the active points on the protective film not binding with thelubricant compound a with a high molecular weight and as a result, thedecrease in the active points on the protective film not binding witheither of the lubricant compound a or the compound b suppressesadsorption of organic contamination cannot be fully obtained.

The molecular weight of the lubricant compound a according to thepresent invention is not particularly limited, but the number averagemolecular weight (Mn) is preferably within a range of 1000 to 10000, forexample, or more preferably within a range of 1000 to 6000. That isbecause repairability by appropriate viscosity is provided, andfavorable lubrication performances are exerted.

A method of molecular weight fractionation is not particularly limited,and molecular weight fractionation using a gel permeation chromatography(GPC) method or molecular weight fractionation using a supercriticalextraction method can be used, for example.

According to this embodiment, the lubricant compound contained in thelubrication layer preferably contains, in short, two types of compounds,that is, a compound with a high molecular weight having aperfluoropolyether main chain in the structure and a compound with a lowmolecular weight, and these two types of compounds are preferably thecompound a with a high molecular weight having a hydroxyl group at theend and the compound b with a molecular weight lower than the compounda, that is, with a number average molecular weight smaller than thecompound a and of not more than 1500. In this embodiment, the molecularweight distribution of the two types of the compounds in total ispreferably within the range of 1 to 1.2. And the content of the compoundb in these two types of the compounds is particularly preferably notmore than 10%.

A method of forming a film of the lubrication layer using the abovelubricant in this embodiment is similar to the first embodimentdescribed above.

Also, the film thickness of the lubrication layer is also preferably 5to 20 Å similarly to the first embodiment.

Third Embodiment

A magnetic disk according to a third embodiment of the present inventionis a magnetic disk in which at least a magnetic layer, a protectivelayer, and a lubrication layer are sequentially provided on a substrateand the lubrication layer is characterized in that a film of a lubricantis formed containing a lubricant compound a and a compound c obtained byreaction between a compound b expressed by the following chemicalformula:

[Chemical formula 12]CF₃(—O—C₂F₄)m—(O—CF₂)n—OCF₃ [m and n in the formula are naturalnumbers.]

and aluminum oxide.

The lubricant compound a contained in the lubrication layer in themagnetic disk of this embodiment is a perfluoropolyether compound havinga perfluoropolyether main chain in the structure and also having ahydroxyl group at the end, and a compound expressed as the followingchemical formula:

[p and q in the formula are natural numbers.]

is favorably cited.

The above exemplary compound of the lubricant compound a contained inthe lubrication layer in the magnetic disk of the present invention is aperfluoropolyether compound having a perfluoropolyether main chain inthe structure and also having four hydroxyl groups at the end. Also, asthe lubricant compound a according to the present invention, aperfluoropolyether compound having a perfluoropolyether main chain inthe structure and having two hydroxyl groups at the end can be alsoused. As these perfluoropolyether lubricants, commercial productsincluding Fomblin Z-TETRAOL (product name) and Fomblin Z DOL (productname) by SOLVAY SOLEXIS, Inc., for example, can be used.

Also, the compound c contained in the lubricant in order to form thelubrication layer in the present invention is obtained by reactionbetween the compound b expressed by the following chemical formula:

[Chemical formula 14]CF₃(—O—C₂F₄)m—(O—CF₂)n—OCF₃

[m and n in the formula are natural numbers.]

and aluminum oxide. That is, by mixing the above compound b (with theweight average molecular weight of approximately 3000 to 7000, forexample) and aluminum oxide (alumina, Al₂O₃) with an appropriate mixingratio and heating them, C—C link of the main chain in the compound b iscut off, and the compound c with a lower molecular weight is obtained.Aluminum oxide is refined and removed.

The molecular weight of the above compound c is not particularly limitedas long as it is obtained by reaction between the above compound b andaluminum oxide and has a lower molecular weight, but in order that theworking effect of the present invention is favorably exerted, the numberaverage molecular weight (Mn) is preferably within a range of not morethan 1500, for example, or more preferably within a range of 500 to1500.

In the present invention, as the lubricant that forms a lubricationlayer, the above lubricant compound a and the above compound c are mixedin use. A mixing ratio when being used in a mixture is preferably suchthat a weight ratio of the lubricant compound a/compound c is within arange of approximately 8:2 to 9:1. If the rate of the lubricant compounda in the lubricant is smaller than the above range, favorablelubrication performances might not be obtained. Also, if the rate of thecompound c in the lubricant is smaller than the above range, the workingthat the compound c with a low molecular weight binds with the activepoints on the protective film not binding with the lubricant compound awith a high molecular weight and as a result, the decrease in the activepoints on the protective film not binding with either of the lubricantcompound a or the compound c suppresses adsorption of organiccontamination effect cannot be fully obtained.

The molecular weight of the lubricant compound a according to thepresent invention is not particularly limited, but the number averagemolecular weight (Mn) is preferably within a range of 1000 to 10000, forexample, or more preferably within a range of 1000 to 6000. That isbecause repairability by appropriate viscosity is provided, andfavorable lubrication performances are exerted.

Also, the above compound b can be obtained from commercial products. Themolecular weight is not particularly limited, but if a commercialproduct is used, by appropriate molecular weight fractionation, thosehaving the weight average molecular weight of approximately 3000 to7000, for example, are appropriate.

A method of molecular weight fractionation is not particularly limited,and molecular weight fractionation using a gel permeation chromatography(GPC) method or molecular weight fractionation using a supercriticalextraction method can be used, for example.

According to this embodiment, the lubricant compound contained in thelubrication layer contains, in short, two types of compounds, that is, acompound with a high molecular weight having a perfluoropolyether mainchain in the structure and a compound with a low molecular weight, andthese two types of compounds are the compound a with a high molecularweight having a hydroxyl group at the end and the compound c with amolecular weight lower than the compound a, that is, with a numberaverage molecular weight smaller than the compound a and preferably ofnot more than 1500. In this embodiment, the molecular weightdistribution of the two types of the compounds in total is preferablywithin the range of 1 to 1.2. And the content of the compound c in thesetwo types of the compounds is particularly preferably not more than 10%.

A method of forming a film of the lubrication layer using the abovelubricant in this embodiment is similar to the first embodimentdescribed above.

Also, the film thickness of the lubrication layer is also preferably 5to 20 Å similarly to the first embodiment.

Also, in the above-described first to third embodiments, as theprotective layer, a carbon protective layer can be favorably used.Particularly, an amorphous carbon protective layer is preferable. Byusing the carbon protective layer as the protective layer, aninteraction between a polar group (particularly a hydroxyl group) of thelubricant according to the present invention and the protective layer isfurther increased, and the working effect by the present invention isfurther exerted, which is a preferable mode.

In the carbon protective layer in the present invention, it ispreferable that nitrogen is contained in the lubrication layer side ofthe protective layer so as to have a composition graded layer in whichhydrogen is contained in the magnetic layer side, for example.

If the carbon protective layer is used in the present invention, a filmcan be formed by using a DC magnetron sputtering method, for example,but an amorphous carbon protective layer formed by the plasma CVD methodis particularly preferable. By forming a film by the plasma CVD method,the surface of the protective layer is made uniform and closely formed.Therefore, to form a lubrication layer according to the presentinvention on the protective layer formed by using the CVD method withsmaller coarseness is preferable.

In the present invention, the film thickness of the protective layer ispreferably 20 to 70 Å. If the thickness is less than 20 Å, performancesas the protective layer might be lowered. The thickness exceeding 70 Åis not preferable from the viewpoint of film thinning.

In the magnetic disk of the present invention, the substrate ispreferably a glass substrate. A glass substrate is rigid and isexcellent in smoothness, which is preferable for higher recordingdensity. As the glass substrate, an aluminosilicate glass substrate, forexample, can be cited, and particularly a chemically-reinforcedaluminosilicate glass substrate is preferable.

In the present invention, regarding coarseness of the main surface ofthe above substrate, the surface is supersmooth with Rmax preferably at6 nm or less and Ra preferably at 0.6 nm or less. The surface coarsenessRmax and Ra here are based on the specification by JIS B0601.

The magnetic disk of the present invention is provided at least with amagnetic layer, a protective layer, and a lubrication layer on thesubstrate, but in the present invention, the magnetic layer is notparticularly limited and may be either an in-plane recording typemagnetic layer or a perpendicular recording type magnetic layer, but theperpendicular recording type magnetic layer is particularly preferablefor realization of the recent rapid increase in recording density.Particularly, a CoPt magnetic layer is preferable since it can obtainboth a high magnetic coercive force and a high reproduction output.

In the magnetic disk of the present invention, an underlayer can beprovided between the substrate and the magnetic layer as necessary.Also, an adhesion layer or a soft magnetic layer or the like may beprovided between the underlayer and the substrate. In this case, as theunderlayer, a Cr layer, a Ta layer, a Ru layer or an alloy layer ofCrMo, CoW, CrW, CrV, CrTi and the like can be cited, and as the adhesionlayer, an alloy layer of CrTi, NiAl, AlRu and the like can be cited, forexample. Also, as the soft magnetic layer, a CoZrTa alloy layer film,for example, can be cited.

As a perpendicular magnetic recording disk suitable for higher recordingdensity, a configuration provided with an adhesion layer, a softmagnetic layer, an underlayer, a magnetic layer (perpendicular magneticrecording layer), a carbon protective layer, and a lubrication layer ona substrate is preferable. In this case, an auxiliary recording layermay be preferably provided on the perpendicular magnetic recording layerthrough an exchange-coupling control layer.

The magnetic disk of the present invention is preferable as a magneticdisk mounted particularly on a LUL-method magnetic disk device. Afurther decrease of the magnetic-head floating amount realized byintroduction of the LUL method has required the magnetic disk to operatestably even with a low floating amount of not more than 10 nm, and themagnetic disk of the present invention having high reliability under thelow floating amount is preferable.

EXAMPLES

The present invention will be described below in more detail byreferring to examples.

The following example 1 and example 2 are examples corresponding to theabove-described first embodiment.

Example 1

FIG. 1 is a magnetic disk 10 according to an embodiment of the presentinvention.

The magnetic disk 10 has an adhesion layer 2, a soft magnetic layer 3, afirst underlayer 4, a second underlayer 5, a magnetic layer 6, a carbonprotective layer 7, and a lubrication layer 8 sequentially formed on thesubstrate 1.

(Manufacture of Lubricant)

By making 2 equivalent weight of the perfluorodiol compound expressed bythe above formula (II) react with 1 equivalent weight of the exemplifieddiepoxy compound under a base condition, the exemplified compound of thelubricant compound (III) of the present invention was manufactured.Specifically, the above both compounds were stirred in acetone, sodiumhydroxide was added and the mixture was further refluxed. Conditionssuch as a reaction temperature, time and the like were set asappropriate.

The lubricant made of the compound obtained as above was subjected tomolecular weight fractionation by the supercritical extraction methodand prepared so that the number average molecular weight measured by theNMR method is 3000, the molecular weight distribution (weight averagemolecular weight (Mw)/number average molecular weight (Mn) ratio) iswithin a range of 1 to 1.2, and a content of the compound with thenumber average molecular weight of not more than 1500 is not more than10%.

(Manufacture of Magnetic Disk)

A 2.5-inch glass disk (outer diameter of 65 mm, inner diameter of 20 mm,and disk thickness of 0.635 mm) made of chemically reinforcedaluminosilicate glass was prepared and used as a disk substrate 1. Themain surface of the disk substrate 1 was mirror-polished so as to have Rmax of 2.13 nm and Ra of 0.20 nm.

On this disk substrate 1, a Ti adhesion layer 2, a Fe soft magneticlayer 3, a NiW first underlayer 4, a Ru second underlayer 5, and aCoCrPt magnetic layer 6 were formed sequentially in an Ar gas atmosphereby the DC magnetron sputtering method. This magnetic layer was aperpendicular magnetic recording type magnetic layer.

Subsequently, a film of a diamond-like carbon protective layer 7 wasformed with the film thickness of 50 Å by the plasma CVD method.

Subsequently, a lubrication layer 8 was formed as follows.

A solution in which the lubricant made of the lubricant (the aboveexemplary compound) of the present invention manufactured as above andsubjected to molecular weight fractionation by the supercriticalextraction method was dispersed and dissolved with concentration of 0.2weight % in Vertrel XF (product name) by DU PONT-MITSUI FLUOROCHEMICALSCOMPANY, LTD., which is a fluorine solvent was, prepared. By using thissolution as an application liquid, the magnetic disk on which films wereformed up to the protective layer 7 was immersed and the liquid wasapplied by the dip method, and a film of the lubrication layer 8 wasformed.

After the film formation, the magnetic disk was subjected to heatingtreatment in a vacuum firing furnace at 130° C. for 90 minutes. The filmthickness of the lubrication layer 8 was measured by a Fourier transforminfrared spectrophotometer (FTIR), and the result was 12 Å. A magneticdisk 10 of Example 1 was obtained as above.

Subsequently, the magnetic disk of Example 1 was evaluated using thefollowing test methods.

(Evaluation of Magnetic Disk)

-   -   (1) First, a CFT characteristic evaluation test (fixed-position        floating test) was conducted.

The magnetic disk obtained as above was left in a Si gas atmosphere inadvance for 24 hours before the test was conducted. A fixed position wasset on the disk inner peripheral side (disk-radius 15 mm position). Inorder to conduct the CFT test in an extreme environment, the test wasconducted in an environment with a temperature at 70° C. and relativehumidity of 80%.

As a result, the magnetic disk of Example 1 was found to endurefixed-point continuous floating for successive four weeks and found tobe extremely excellent in the CFT characteristics even under an extremecondition. Also, the surfaces of the magnetic head and the magnetic diskafter the CFT test were examined in detail by an optical microscope andan electronic microscope, but no scar or corrosion phenomenon wasobserved.

(2) Subsequently, in order to evaluate LUL (Load-Unload) durability ofthe magnetic disk, a LUL durability test was conducted.

An LUL-type HDD (5400-rpm rotation type) was prepared, and a magnetichead with a floating amount of 5 nm and a magnetic disk of the examplewere mounted. A slider of the magnetic head was a NPAB (negativepressure) slider, and on a reproducing element, a magnetoresistanceeffect type element (GMR element) was mounted. An FeNi permalloy alloywas used as a shield portion. By making this LUL-type HDD repeat acontinuous LUL operation, the number of LUL times the magnetic diskendured until a failure occurred was measured.

As a result, the magnetic disk of Example 1 endured 700 thousand timesof the LUL operation without a failure under the super-low floatingamount of 5 nm, and no fly stiction failure occurred. Under a usual HDDuse environment, it is said to take approximately 10 years for themagnetic disk to exceed the number of the LUL times of 400 thousands,and endurance of 600 thousand is considered as favorable at the present,and thus, the magnetic disk of Example 1 can be considered to haveextremely high reliability.

The surface of the magnetic disk after the LUL durability test wasexamined in detail by an optical microscope and an electronicmicroscope, but no abnormality such as a scar or a stain was observedand the surface was favorable. Also, the surface of the magnetic headafter the LUL durability test was examined in detail by an opticalmicroscope and an electronic microscope, but no abnormality such as ascar or a stain was observed or no adhesion of the lubricant to themagnetic head or a corrosion failure was observed and the surface wasfavorable.

Example 2

As the lubricant, Fomblin Z-TETRAOL (product name) by SOLVAY SOLEXIS,Inc., which is a perfluoropolyether lubricant, was subjected tomolecular weight fractionation by the GPC method, a compound preparedsuch that the number average molecular weight measured by the NMR methodis 3000, the molecular weight distribution (weight average molecularweight (Mw)/number average molecular weight (Mn) ratio) is within arange of 1 to 1.2, and a content of the compound with the number averagemolecular weight of not more than 1500 is not more than 10% was used.The magnetic disk manufactured similarly to Example 1 except this pointwas used as Example 2.

Subsequently, similarly to Example 1, the magnetic disk was exposed tothe Si gas atmosphere and the CFT characteristic evaluation test wasconducted, and as a result, the magnetic disk endured the fixed-pointcontinuous floating for successive four weeks, and it was found out thatthe magnetic disk was extremely excellent in the CFT characteristicseven under the extreme conditions. Also, the surfaces of the magnetichead and the magnetic disk after the CFT test were examined in detail byan optical microscope and an electronic microscope, but no scar orcorrosion phenomenon was observed.

Also, the LUL durability test was conducted similarly to Example 1, andas a result, the magnetic disk of Example 2 endured 700 thousand timesof the LUL operation without a failure under the super-low floatingamount of 5 nm, and no fly stiction failure occurred. The magnetic diskof Example 2 can be considered to have extremely high reliability.

The surface of the magnetic disk after the LUL durability test wasexamined in detail by an optical microscope and an electronicmicroscope, but no abnormality such as a scar or a stain was observedand the surface was favorable. Also, the surface of the magnetic headafter the LUL durability test was examined in detail by an opticalmicroscope and an electronic microscope, but no abnormality such as ascar or a stain was observed or no adhesion of the lubricant to themagnetic head or a corrosion failure was observed and the surface wasfavorable.

Comparative Example

As the lubricant, Fomblin Z-TETRAOL (product name) by SOLVAY SOLEXIS,Inc., which is a perfluoropolyether lubricant, was subjected tomolecular weight fractionation by the GPC method, a compound with Mw of3000 and a molecular-weight dispersion degree of 1.08 was used. The lowmolecular weight region side was removed by this molecular weightfractionation, and those having the number average molecular weight ofnot more than 1500 were not contained. A solution obtained by dispersingand dissolving this in Vertrel XF (product name) by DU PONT-MITSUIFLUOROCHEMICALS COMPANY, LTD., which is a fluorine solvent, was used asan application liquid, a magnetic disk on which films were formed up tothe protective layer is immersed, and the liquid was applied by the dipmethod so as to form a lubricant layer. Here, concentration of theapplication liquid was adjusted as appropriate, and the film was formedso that the lubrication layer film thickness was within a range of 10 to12 Å. The magnetic disk manufactured similarly to Example 1 other thanthe above was used as a comparative example.

Subsequently, similarly to Example, the magnetic disk was exposed to theSi gas atmosphere and the CFT characteristic evaluation test wasconducted, and as a result, the magnetic disk failed in less thansuccessive four weeks. This was considered to be caused by active pointsremaining on the surface of the protective layer not binding with thelubricant, which adsorbed the organic gas in the atmosphere and becamehead contamination.

Also, similarly to the example, as the result of the LUL durability testunder the super-low floating amount of 5 nm, a fly stiction failureoccurred in the middle in the magnetic disk of this Comparative Exampleand failed by head crush at 300 thousand times. The surface of themagnetic disk after the LUL durability test was examined in detail by anoptical microscope and an electronic microscope, and a number of scarsand the like were observed. Also, the surface of the magnetic head afterthe LUL durability test was examined in detail by an optical microscopeand an electronic microscope, and adhesion of the lubricant to themagnetic head and corrosion failures were observed.

The following Example 3 is an example corresponding to theabove-described second embodiment.

Example 3

(Preparation of Lubricant)

As a lubricant containing the lubricant compound a, Fomblin Z-TETRAOL(product name) by SOLVAY SOLEXIS, Inc., which is a commercialperfluoropolyether lubricant, was subjected to molecular weightfractionation by the GPC method, a compound with Mw of 3000 and amolecular-weight dispersion degree of 1.08 was used.

Also, the above exemplary compound (2) of the compound b wasmanufactured as follows.

A base in 2 equivalent amounts was reacted with a perfluoropolyethercompound having a perfluoropolyether main chain in a molecule and then,glycidyl phenyl ether in 2 equivalent amounts was reacted formanufacture. The compound b obtained as above was subjected to molecularweight fractionation as appropriate by the supercritical extractionmethod and the compound with Mn of not more than 1500 was used.

And the lubricant compound a and the compound b obtained as above weremixed at a weight ratio of 9:1, and a lubricant used in this example wasprepared.

(Manufacture of Magnetic Disk)

A 2.5-inch glass disk (outer diameter of 65 mm, inner diameter of 20 mm,and disk thickness of 0.635 mm) made of chemically reinforcedaluminosilicate glass was prepared and used as a disk substrate 1. Themain surface of the disk substrate 1 was mirror-polished so as to have Rmax of 2.13 nm and Ra of 0.20 nm.

On this disk substrate 1, a Ti adhesion layer 2, a Fe soft magneticlayer 3, a NiW first underlayer 4, a Ru second underlayer 5, and aCoCrPt magnetic layer 6 were formed sequentially in an Ar gas atmosphereby the DC magnetron sputtering method. This magnetic layer was aperpendicular magnetic recording type magnetic layer.

Subsequently, a film of a diamond-like carbon protective layer 7 wasformed with the film thickness of 50 Å by the plasma CVD method.

Subsequently, a lubrication layer 8 was formed as follows.

A solution in which the lubricant prepared as above was dispersed anddissolved with concentration of 0.2 weight % in Vertrel XF (productname) by DU PONT-MITSUI FLUOROCHEMICALS COMPANY, LTD., which is afluorine solvent, was prepared. By using this solution as an applicationliquid, the magnetic disk on which films up to the protective layer 7were formed was immersed and the liquid was applied by the dip methodand a film of the lubrication layer 8 was formed. After the filmformation, the magnetic disk was subjected to heating treatment in avacuum firing furnace at 130° C. for 90 minutes. The film thickness ofthe lubrication layer 8 was measured by a Fourier transform infraredspectrophotometer (FTIR), and the result was 12 Å. Thus, the magneticdisk of Example 3 was obtained.

Subsequently, the magnetic disk of Example 3 was evaluated by the testmethod similar to that of Example 1.

First, a CFT characteristic evaluation test (fixed-position floatingtest) was conducted, and as a result, the magnetic disk of Example 3 wasfound to be able to endure fixed-point continuous floating forsuccessive four weeks and to be extremely excellent in the CFTcharacteristics even under an extreme condition. Also, the surfaces ofthe magnetic head and the magnetic disk after the CFT test were examinedin detail by an optical microscope and an electronic microscope, but noscar or corrosion phenomenon was observed.

As the result of the LUL durability test, the magnetic disk of Example 3endured 800 thousand times of the LUL operation without a failure underthe super-low floating amount of 5 nm, and no fly stiction failureoccurred. The magnetic disk of Example 3 can be considered to haveextremely high reliability. The surface of the magnetic disk after theLUL durability test was examined in detail by an optical microscope andan electronic microscope, but no abnormality such as a scar or a stainwas observed and the surface was favorable. Also, the surface of themagnetic head after the LUL durability test was examined in detail by anoptical microscope and an electronic microscope, but no abnormality suchas a scar or a stain was observed or no adhesion of the lubricant to themagnetic head or a corrosion failure was observed and the surface wasfavorable.

The following Example 4 is an example corresponding to theabove-described third embodiment.

Example 4

(Preparation of Lubricant)

As a lubricant containing the lubricant compound a, Fomblin Z-TETRAOL(product name) by SOLVAY SOLEXIS, Inc., which is a commercialperfluoropolyether lubricant, was subjected to molecular weightfractionation by the GPC method, a compound with Mw of 3000 and amolecular-weight dispersion degree of 1.08 was used.

Also, a commercial product of the above compound b and alumina (Al₂O₃)were mixed at an appropriate mixing ratio and heated so as to obtain thecompound c. The above-described alumina was removed by refining.

Then, the lubricant compound a and the compound c obtained as above weremixed at a weight ratio of 9:1, and a lubricant used in this example wasprepared.

(Manufacture of Magnetic Disk)

A 2.5-inch glass disk (outer diameter of 65 mm, inner diameter of 20 mm,and disk thickness of 0.635 mm) made of chemically reinforcedaluminosilicate glass was prepared and used as a disk substrate 1. Themain surface of the disk substrate 1 was mirror-polished so as to have Rmax of 2.13 nm and Ra of 0.20 nm.

On this disk substrate 1, a Ti adhesion layer 2, a Fe soft magneticlayer 3, a NiW first underlayer 4, a Ru second underlayer 5, and aCoCrPt magnetic layer 6 were formed sequentially in an Ar gas atmosphereby the DC magnetron sputtering method. This magnetic layer was aperpendicular magnetic recording type magnetic layer.

Subsequently, a film of a diamond-like carbon protective layer 7 wasformed with the film thickness of 50 Å by the plasma CVD method.

Subsequently, a lubrication layer 8 was formed as follows.

A solution in which the lubricant prepared as above was dispersed anddissolved with concentration of 0.2 weight % in Vertrel XF (productname) by DU PONT-MITSUI FLUOROCHEMICALS COMPANY, LTD., which is afluorine solvent was, prepared. By using this solution as an applicationliquid, the magnetic disk on which films were formed up to theprotective layer 7 was immersed and the liquid was applied by the dipmethod and a film of the lubrication layer 8 was formed.

After the film formation, the magnetic disk was subjected to heatingtreatment in a vacuum firing furnace at 130° C. for 90 minutes. The filmthickness of the lubrication layer 8 was measured by a Fourier transforminfrared spectrophotometer (FTIR), and the result was 12 Å. Thus, amagnetic disk of Example 4 was obtained as above.

Subsequently, the magnetic disk of Example 4 was evaluated by the testmethod similar to that of Example 1.

First, a CFT characteristic evaluation test (fixed-position floatingtest) was conducted, and as a result, the magnetic disk of Example 4 wasfound to be able to endure fixed-point continuous floating forsuccessive four weeks and to be extremely excellent in the CFTcharacteristics even under an extreme condition. Also, the surfaces ofthe magnetic head and the magnetic disk after the CFT test were examinedin detail by an optical microscope and an electronic microscope, but noscar or corrosion phenomenon was observed.

Subsequently, as the result of the LUL durability test, the magneticdisk of Example 4 endured 700 thousand times of the LUL operationwithout a failure under the super-low floating amount of 5 nm, and nofly stiction failure occurred. The magnetic disk of Example 4 can beconsidered to have extremely high reliability. The surface of themagnetic disk after the LUL durability test was examined in detail by anoptical microscope and an electronic microscope, but no abnormality suchas a scar or a stain was observed and the surface was favorable. Also,the surface of the magnetic head after the LUL durability test wasexamined in detail by an optical microscope and an electronicmicroscope, but no abnormality such as a scar or a stain was observed orno adhesion of the lubricant to the magnetic head or a corrosion failurewas observed and the surface was favorable.

The following Examples 5 and 6 are examples corresponding to theabove-described second embodiment.

Example 5

(Preparation of Lubricant)

As a lubricant containing the lubricant compound a, Fomblin Z-TETRAOL(product name) by SOLVAY SOLEXIS, Inc., which is a commercialperfluoropolyether lubricant, was subjected to molecular weightfractionation by the GPC method, a compound with Mw of 2500 and amolecular-weight dispersion degree of 1.08 was used.

Also, the exemplary compound (3) of the compound b was manufactured asfollows.

A base in 2 equivalent amounts was reacted with a perfluoropolyethercompound having a perfluoropolyether main chain in a molecule and then,glycidyl phenyl ether in 2 equivalent amounts was reacted formanufacture. The compound b obtained as above was subjected to molecularweight fractionation as appropriate by the supercritical extractionmethod and the compound with Mn of not more than 1500 was used.

And the lubricant compound a and the compound b obtained as above weremixed at a weight ratio of 9:1, and a lubricant used in this example wasprepared. The molecular weight distribution of the entire lubricantobtained by mixing the compound a and the compound b as above was withina range of 1 to 1.2.

The magnetic disk manufactured similarly to Example 3 other than theabove points was used as Example 5.

Subsequently, similarly to Example 1, as the result of the CFTcharacteristic evaluation test, the magnetic disk of this Example wasfound to be able to endure fixed-point continuous floating forsuccessive four weeks and to be extremely excellent in the CFTcharacteristics even under an extreme condition. Also, the surfaces ofthe magnetic head and the magnetic disk after the CFT test were examinedin detail by an optical microscope and an electronic microscope, but noscar or corrosion phenomenon was observed.

Also, similarly to Example 1, as the result of the LUL durability test,the magnetic disk of Example 5 endured 800 thousand times of the LULoperation without a failure under the super-low floating amount of 5 nm,and no fly stiction failure occurred. The magnetic disk of Example 5 canbe considered to have extremely high reliability.

The surface of the magnetic disk after the LUL durability test wasexamined in detail by an optical microscope and an electronicmicroscope, but no abnormality such as a scar or a stain was observedand the surface was favorable. Also, the surface of the magnetic headafter the LUL durability test was examined in detail by an opticalmicroscope and an electronic microscope, but no abnormality such as ascar or a stain was observed or no adhesion of the lubricant to themagnetic head or a corrosion failure was observed and the surface wasfavorable.

Example 6

(Preparation of Lubricant)

As a lubricant containing the lubricant compound a, Fomblin Z-TETRAOL(product name) by SOLVAY SOLEXIS, Inc., which is a commercialperfluoropolyether lubricant, was subjected to molecular weightfractionation by the GPC method, a compound with Mw of 3000 and amolecular-weight dispersion degree of 1.08 was used.

Also, the exemplary compound (1) of the compound b was manufactured asfollows.

A base in 2 equivalent amounts was reacted with a perfluoropolyethercompound having a perfluoropolyether main chain in a molecule and then,glycidyl phenyl ether in 2 equivalent amounts was reacted formanufacture. The compound b obtained as above was subjected to molecularweight fractionation as appropriate by the supercritical extractionmethod and the compound with Mn of not more than 1500 was used.

And the lubricant compound a and the compound b obtained as above weremixed at a weight ratio of 9:1, and a lubricant used in this example wasprepared. The molecular weight distribution of the entire lubricantobtained by mixing the compound a and the compound b as above was withina range of 1 to 1.2.

The magnetic disk manufactured similarly to Example 3 other than theabove points was used as Example 6.

Subsequently, similarly to Example 1, as the result of the CFTcharacteristic evaluation test, the magnetic disk of this Example wasfound to be able to endure fixed-point continuous floating forsuccessive four weeks and to be extremely excellent in the CFTcharacteristics even under an extreme condition. Also, the surfaces ofthe magnetic head and the magnetic disk after the CFT test were examinedin detail by an optical microscope and an electronic microscope, but noscar or corrosion phenomenon was observed.

Also, similarly to Example 1, as the result of the LUL durability test,the magnetic disk of Example 6 endured 800 thousand times of the LULoperation without a failure under the super-low floating amount of 5 nm,and no fly stiction failure occurred. The magnetic disk of Example 6 canbe considered to have extremely high reliability.

The surface of the magnetic disk after the LUL durability test wasexamined in detail by an optical microscope and an electronicmicroscope, but no abnormality such as a scar or a stain was observedand the surface was favorable. Also, the surface of the magnetic headafter the LUL durability test was examined in detail by an opticalmicroscope and an electronic microscope, but no abnormality such as ascar or a stain was observed or no adhesion of the lubricant to themagnetic head or a corrosion failure was observed and the surface wasfavorable.

As described above, in Examples of the present invention, the magneticdisk with high reliability can be obtained which is excellent in thedurability of the magnetic disk or particularly excellent in the LULdurability and the CFT characteristics, and under the lower floatingamount of the magnetic head accompanying the recent rapid increase in arecording density and under the extremely severe environmentalresistance accompanying the diversification of applications.

REFERENCE SIGNS LIST

-   -   1 substrate    -   2 adhesion layer    -   3 soft magnetic layer    -   4 first underlayer    -   5 second underlayer    -   6 magnetic layer    -   7 carbon protective layer    -   8 lubrication layer    -   10 magnetic disk

The invention claimed is:
 1. A magnetic disk comprising a magneticlayer, a protective layer, and a lubrication layer sequentially providedon a substrate, wherein: said lubrication layer comprises a lubricantcomprising: a compound A comprising a perfluoropolyether main chain anda hydroxyl terminal group, wherein the compound A has a number averagemolecular weight of 1000 to 10,000; and a compound C, wherein thecompound C is obtained from a reaction between aluminum oxide and acompound B expressed by formula I:CF₃(—O—C₂F₄)_(m)—(O—CF₂)_(n)—OCF₃  formula I wherein m and n are naturalnumbers not less than 1; wherein: the aluminum oxide is removed afterthe reaction, and the compound C consists of fragments resulting from acleavage of a carbon-carbon bond in the compound B and has a numberaverage molecular weight less than compound A and not more than
 1500. 2.The magnetic disk according to claim 1, wherein the compound A has anumber average molecular weight of 1000 to
 6000. 3. The magnetic diskaccording to claim 1, wherein said protective layer is a carbonprotective layer.
 4. The magnetic disk according to claim 1, wherein themagnetic disk is a magnetic disk mounted on a Load-Unload methodmagnetic disk device.
 5. The magnetic disk according to claim 1, whereinsaid compound A and said compound C have a weight ratio of 8:2 to 9:1.6. The magnetic disk according to claim 1, wherein said compound B has amolecular weight of 3000 to
 7000. 7. The magnetic disk according toclaim 1, wherein the lubrication layer has a film thickness of 5 to 20Å.
 8. The magnetic disk according to claim 1, wherein the protectivelayer has a film thickness of 20 to 70 Å.
 9. The magnetic disk accordingto claim 1, wherein the compound A has two terminal hydroxyl groups. 10.The magnetic disk according to claim 1, wherein the compound A has achemical formula:

wherein p and q are natural numbers not less than
 1. 11. The magneticdisk according to claim 1, wherein the compound C has a number averagemolecular weight of 500 to 1500.